1. Field of the Invention
The present invention relates generally to a method and a system for accurately locating the welded seam of a seam-welded metal pipe. More specifically, the invention relates to a method and system for locating the seam in a seam-welded metal pipe optically by means of a laser beam. In addition, the invention relates to a method and system for inspecting the welded seam in the seam-welded pipe following location thereof by means of the seam locating system according to the invention.
2. Description of the Prior Art
The manufacture of seam-welded pipe requires numerous treatment steps and tests on the produced pipe. Such treatment includes annealing of the welded seam and such tests include inspection of the seams. Seam annealing and inspection require accurate location of the finished seam in the seam-welded pipe.
Before the welding bead is removed from the seam, the seam is relatively easy to find because of the unevenness of the outer pipe surface. However, after removing the welding bead, it becomes more difficult to locate the seam since the pipe surface is then essentially smooth. On the other hand, in the seam-welded pipe industry, it is normal during manuafacture to remove the welding bead during welding. Therefore, when the pipe is transferred for annealing and seam inspection, the welding bead is already removed. This makes it difficult to find the seam.
Conventionally, various approaches have been proposed for accurate location of the seam of a seam-welded metal pipe. One approach is to optically locate the seam by means of a light beam or laser beam. This seam position locating process and/or system was proposed in the Japanese Patent First Publication (Tokkai) Showa No. 59-108903, published on June 23, 1984, which has been assigned to the owner of the present invention. In the system disclosed, a laser beam is irradiated onto the outer surface of the seam-welded metal pipe. The reflected beam is received and analyzed to distinguish between unwelded section of the pipe and the seam depending upon changes in the intensity and/or orientation of the reflected beam. This system is effective for locating the seams on a seam-welded metal pipe. This system is especially effective for accurately locating the seams before annealing.
However, a difficulty is encountered after annealing since the surface of the pipe tends to be marred by scale marks, scratch marks and so forth during the annealing process. Such scale marks, scratches and so forth make it more difficult to optically distinguish between the seam and the unwelded sections. Since seam inspection is usually performed after seam annealing, some difficulty in accurately locating the seam for inspection persists.